With reference to FIG. 1, a control system may include a control knob 12 associated with a panel or substrate 14, a magnet 16 fixedly disposed in the control knob for rotation with the knob, and a magnetic encoder 18 fixedly disposed on the panel or substrate or to a circuit carrier 20 attached to the panel or substrate. The control knob 12 has an axis of rotation A passing through the center of the knob. The magnet 16 and magnetic encoder 18 are disposed along or immediately adjacent the axis of rotation A.
The magnet 16 has north and south poles N, S, and it produces a magnetic field extending between the north and south poles. Magnetic flux lines F leave the magnet 16 from the north pole N and return to the magnet at the south pole S. The flux lines F pass through the encoder 18 generally perpendicular to the axis of rotation A. Because the magnet 16 is fixedly disposed in the knob 12, rotation of the knob results in rotation of the magnet. Rotation of the magnet 16 results in rotation of the magnetic field and the flux lines F about the axis of rotation A. The magnetic encoder 18 responds to rotation of the flux lines F passing there through by outputting a signal or signals that may be indicative of the direction, speed, and/or degree of rotation of the flux lines F passing there through and, therefore, indicative of the direction, speed, and/or degree of rotation of the knob 12.
Because the magnet 16 is disposed along or immediately adjacent the axis of rotation A, which passes through the center of the knob 12, it is impractical to provide a display at the center of the knob along the axis of rotation A. With reference to FIG. 2, attempts have been made to offset the magnet 16 from the center of the knob 12 to the perimeter of the knob, thereby making available space for a display proximate the center of the knob along the axis of rotation A. Locating the magnet 16 in this manner, distant from the axis of rotation and offset from the encoder, however, alters the orientation of the flux lines F through the encoder 18 in a manner that adversely affects the operation of the encoder.